Electrical power supply systems are known which incorporate detectors adapted to detect and circumvent electrical arc faults or transients. Arc faults/transient events may manifest themselves as impulses of current and/or voltage in excess of the rating of individual components of the power supply system. Without intervention, such arc faults/transients are potentially damaging to wiring and downstream loads of the power supply system. The damage may not be confined to the power supply system directly experiencing the arc fault/transient event, but may propagate to other systems nearby (for example, due to an excessive heat build-up which can result from an arc fault/transient). Additionally, such arc fault/transient events are also hazardous to a user of the power supply system. For the purpose of this document, the terms “detector” and “arc fault/transient detector” are used interchangeably.
It is known for circuit breakers to be used in industrial and domestic applications to protect against the effects of electrical arc faults and transients, with the circuit breaker providing an automatically operated breaker switch designed to trip upon detection of a fault condition and thereby interrupt current flow to protect electrical components downstream of the circuit breaker from consequent damage. Known in the field of semi-conductors are solid state power controllers (SSPC). SSPC's are used for controlling voltage and/or current supplied to a load and incorporate circuitry for identifying overload conditions. In essence, an SSPC functions as a form of circuit breaker, incorporating a breaker switch and a detector for detecting an arc fault or transient and thereby acting to open (“trip”) the breaker switch.
In the art outlined above, the ability to trip a breaker switch is dependent upon proper functioning of the arc fault/transient detector. Fault conditions in the detector can manifest themselves as a failure to detect the presence of the occurrence of an arc fault/transient, which may result in the breaker switch failing to trip and the risk of the load and the user being exposed to potentially dangerous electric current and voltage levels. Furthermore, as indicated above, there is a risk of the arc fault/transient event causing indirect damage and faults to adjacent systems. Detection failures can have disastrous safety implications; for example, in the case of an aircraft incorporating electrical power supply systems including such detectors and breaker switches to detect and nullify the effects of any arc faults/transients, failure to detect a fault and trip the flow of current from the power source would risk fire and loss of an aircraft. Fault conditions in a detector can also manifest themselves as indicating the presence of an arc fault/transient where no such arc fault/transient exists—the resulting tripping of the breaker switch is referred to herein as a “nuisance trip”. It is highly desired for such nuisance trips to be avoided because they unnecessarily interrupt the continued operation of loads powered by the power source of the supply system. As well as being inconvenient, where such loads are themselves performing a safety function, such nuisance trips are potentially dangerous as they can lead to unscheduled outages during which the safety function is not available.
Whilst testing of an arc fault/transient detector prior to its installation and commissioning in an electrical power supply system is easy to achieve, such testing does not address any failures or errors in detector functioning which occur during and after installation and commissioning. Although it may be possible to remove a detector from the power supply system after commissioning to enable the detector to be tested away from the system, the removal would increase the duration for which the power supply system is out of use, with time required for removing the detector from the system, testing the detector and then reinstalling the detector within the system. Furthermore, in some applications such detectors may be located in inaccessible or hard to reach locations, thereby further increasing the amount of maintenance time required to remove the detector. An example of inaccessible or hard to reach locations is for electrical power supply systems used in aircraft, with such systems often installed in cramped environments and alongside multiple other aircraft systems.
Given these issues, there is a need for being able to verify correct functioning of an electric arc fault/transient detector without necessitating removal of the detector from an electrical power supply system of which it forms part.